On Tue, Sep 12, 2023 at 06:33:34PM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
>
> Double times of clear_page observed in an arm SOC(A55) when
> CONFIG_INIT_ON_ALLOC_DEFAULT_ON is on, which introduced by
> vma_alloc_zeroed_movable_folio within do_anonymous_pages.
> Since there is no D-cache operation within v6's clear_user_highpage,
> I would like to suggest to remove the redundant clear_page.
>
> struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
> unsigned long vaddr)
> {
> struct folio *folio;
>
> //first clear_page invoked by vma_alloc_folio==>alloc_page==>post_alloc_hook
> folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, vma, vaddr, false);
> if (folio)
> //second clear_page which is meaningless since it do nothing to D-cache in armv6
> clear_user_highpage(&folio->page, vaddr);
This is, of course, not the only place which calls clear_user_highpage().
Please explain why this patch is safe for all the _other_ places which
call clear_user_highpage().
> return folio;
> }
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
> arch/arm/mm/copypage-v6.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/arch/arm/mm/copypage-v6.c b/arch/arm/mm/copypage-v6.c
> index a1a71f36d850..6f8bee1b3203 100644
> --- a/arch/arm/mm/copypage-v6.c
> +++ b/arch/arm/mm/copypage-v6.c
> @@ -9,6 +9,7 @@
> #include <linux/mm.h>
> #include <linux/highmem.h>
> #include <linux/pagemap.h>
> +#include <linux/gfp.h>
>
> #include <asm/shmparam.h>
> #include <asm/tlbflush.h>
> @@ -45,6 +46,13 @@ static void v6_copy_user_highpage_nonaliasing(struct page *to,
> */
> static void v6_clear_user_highpage_nonaliasing(struct page *page, unsigned long vaddr)
> {
> + /*
> + * This criteria only help bailing out when CONFIG_INIT_ON_ALLOC_DEFAULT_ON
> + * is on. The page has been memset to zero when it allocated and the
> + * bellowing clear_page will do it again.
> + */
> + if (want_init_on_alloc(GFP_HIGHUSER_MOVABLE))
> + return;
> void *kaddr = kmap_atomic(page);
> clear_page(kaddr);
> kunmap_atomic(kaddr);
> --
> 2.25.1
>
